Our objectives in the past year have been to conduct experiments having mainly to do with the ontogeny of appetitive learning and extinction, with special emphasis on stages of development of persistence (the partial reinforcement extinction effect, PREE), and other paradoxical effects of appetitive reinforcement: the reward magnitude extinction effect (MREE), the overstraining extinction effect (OEE), and successive negative contract (SNC). At the same time we have begun pilot work on grant-related projects having to to with the effects of artificial rearing, the conditioning of ultrasounds, and the relation of habituation to generalized persistence. We feel that this work is central to an understanding of the development of temperamental-emotional reactions in infancy and early childhood.